Downhole percussion drilling apparatus

ABSTRACT

A downhole percussion drilling apparatus includes a housing and a piston rotatably supported within an interior bore of the housing. A first engagement surface serves as a cam surface. A second engagement surface serves as a follower surface. The cam surface has a plurality of inclined planes each of which terminates in a drop off. With each rotation of the piston, the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston.

FIELD OF THE INVENTION

[0001] The present invention relates to a downhole percussion drillingapparatus

BACKGROUND OF THE INVENTION

[0002] U.S. Pat. No. 5,396,965 (Hall et al 1995) entitled “down-hole mudactuated hammer” and U.S. Pat. No. 5,680,904 (Patterson 1997) entitled“in-the-hole percussion rock drill” both describe downhole percussiondrilling apparatus with reciprocating piston hammers which are adaptedto moved axially in relation to a housing. The piston hammers are movedby drilling mud pumped down the drill string under high pressure.

SUMMARY OF THE INVENTION

[0003] The present invention relates to an alternative downholepercussion drilling apparatus.

[0004] According to the present invention there is provided a downholepercussion drilling apparatus which includes an elongate tubular housingadapted for insertion down a borehole. The housing has an outer surfaceand an inner surface which defines an interior bore. A piston isrotatably supported within the interior bore of the housing. The pistonhas an exterior surface, a first end and a second end. The first end isadapted for connection to a downhole motor assembly that imparts arotary motion to the piston. The second end is adapted for connection toa drill bit assembly. A first engagement surface is non-rotatablycoupled to and projects from the inner surface of the housing into theinterior bore. A second engagement surface is non-rotatably coupled toand projects from the exterior surface of the piston into the interiorbore. One of the first engagement surface and the second engagementsurface serves as a cam surface and the other of the first engagementsurface and the second engagement surface serves as a follower surface.The cam surface has a plurality of inclined planes each of whichterminates in a drop off. With each rotation of the piston, the followersurface rises up each of the inclined planes and then falls down each ofthe drop offs of the cam surface thereby imparting a series ofpercussive hammering impacts to the piston. Springs are provided withinthe interior bore between the inner surface of the housing and the outersurface of the piston to maintain the first engagement surface and thesecond engagement surface engaged during rotation of the piston andallow limited axial travel of the piston relative to the housing duringthe percussive hammering impacts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] These and other features of the invention will become moreapparent from the following description in which reference is made tothe appended drawings, the drawings are for the purpose of illustrationonly and are not intended to in any way limit the scope of the inventionto the particular embodiment or embodiments shown, wherein:

[0006]FIG. 1 is a side elevation view, in section, of a first embodimentof downhole percussion drilling apparatus constructed in accordance withthe teachings of the present invention.

[0007]FIG. 2 is a side elevation view, in section, of the firstengagement surface (cam surface) and the second engagement surface(follower surface) of the downhole percussion drilling apparatusillustrated in FIG. 1.

[0008]FIG. 3 is a front elevation view of the first engagement surface(cam surface) of the downhole percussion drilling apparatus illustratedin FIG. 1.

[0009]FIG. 4 is section view taken along section lines A-A of the firstengagement surface (cam surface) illustrated in FIG. 3.

[0010]FIG. 5 is section view of the first engagement surface (camsurface) illustrated in FIG. 4 engaged with the second engagementsurface (follower surface).

[0011]FIG. 6 is a side elevation view, in section, of an alternativeembodiment of downhole percussion drilling apparatus constructed inaccordance with the teachings of the present invention.

[0012]FIG. 7a is section view of the first engagement surface (camsurface) illustrated in FIG. 5 engaged with the second engagementsurface (follower surface).

[0013]FIG. 7b is section view of the first engagement surface (camsurface) illustrated in FIG. 7a engaged with the second engagementsurface (follower surface) as follower surface begins to rise upinclined planes of cam surface.

[0014]FIG. 7c is section view of the first engagement surface (camsurface) illustrated in FIG. 7a engaged with the second engagementsurface (follower surface) as follower surface continues to rise upinclined planes of cam surface.

[0015]FIG. 7d is section view of the first engagement surface (camsurface) illustrated in FIG. 7a engaged with the second engagementsurface (follower surface) as follower surface begins falls down each ofdrop offs of cam surface.

[0016]FIG. 7e is section view of the first engagement surface (camsurface) illustrated in FIG. 7a engaged with the second engagementsurface (follower surface) where follower surface has fallen down dropoffs of cam surface.

[0017]FIG. 8 is a detailed side elevation view, in section, of ahydraulic damper added to shield the off-bottom bearing from hammeringimpacts.

[0018]FIG. 9 is a detailed side elevation view, in section, of aninternal coupling configuration used to turn the hammering action on andoff, with the hammer action turned on.

[0019]FIG. 10 is a detailed side elevation view, in section, of aninternal coupling configuration used to turn the hammering action on andoff, with the hammer action turned off.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The preferred embodiment, a downhole percussion drillingapparatus generally identified by reference numeral 10, will now bedescribed with reference to FIGS. 1 through 5, and FIGS. 7a through 7 e.An alternative embodiment, generally identified by reference numeral100, will be described with reference to FIG. 6.

[0021] Structure and Relationship of Parts:

[0022] Referring to FIG. 1, there is provided a downhole percussiondrilling apparatus 10, which includes an elongate tubular housing 12adapted for insertion down a borehole. For ease of assembly, housing 12includes a first section 14, a second section 16, a third section 18 anda forth section 20, which are secured together by threaded connectionsto form housing 12. Housing 12 has an outer surface 22 and an innersurface 24 which defines an interior bore 26. A piston 28 is rotatablysupported within interior bore 26 of housing 12. For ease of assembly,piston 28 is formed from a first section 30 and a second section 32.Piston 28 has an exterior surface 34, a first end 36 and a second end38. First end 36 is adapted for connection to a downhole motor assembly40 that imparts a rotary motion to piston 28 and second end 38 isadapted for connection to a drill bit assembly (not shown). A firstsleeve 39 and a second sleeve 41 are positioned in end to end relationoverlying piston 28 within interior bore 26. First sleeve 29 isnon-rotatably coupled to inner surface 24 of housing 12 by means ofspline 43. Spline 43 is best illustrated in FIG. 2. A first engagementsurface or cam surface 42 is positioned at one end 45 of first sleeve39. Referring to FIG. 1, second sleeve 41 is non-rotatably coupled toexterior surface 34 of piston 28 by means of spline 47. Spline 47 isbest illustrated in FIG. 2. A second engagement surface or followersurface 44 is positioned at one end 49 of second sleeve 41.

[0023] Referring to FIG. 3,4 and 5, cam surface 42 has a plurality ofinclined planes 50 each terminating in a drop off 52. Referring to FIGS.7a through 7 e, with each rotation of piston 28 illustrated in FIG. 1,follower surface 48 rises up each of inclined planes 50 and then fallsdown each of drop offs 52 of cam surface 42 thereby imparting a seriesof percussive hammering impacts to piston 28 illustrated in FIG. 1.

[0024] Referring to FIG. 1, a first set of springs 54 are providedwithin interior bore 26 between inner surface 24 of housing 12 andexterior surface 34 of piston 28 to maintain follower surface 42 inengagement with cam surface 44 during rotation of piston 28 and allowlimited axial travel of piston 28 relative to housing 12 during thepercussive hammering impacts. Axial travel of piston 28 is limited tobetween ⅛ to ⅜ of an inch. A second set of springs 56 provide off bottomloading to thrust bearings 70 when downhole percussion drillingapparatus 10 is placed in tension.

[0025] Radial bearings or bushings 58 are disposed between inner surface24 of housing 12 and exterior surface 34 of piston 28, therebytransmitting radial loads from piston 28 to housing 12. Sealingassemblies 60 and 62 are provided a first end 36 of piston 128 to limitentry of abrasive drilling fluids. Sealing assemblies 60 and 62 includeseals 64 positioned in grooves 66 in sealing elements 68 disposed ininterior bore 26. Thrust bearings, generally referenced by numeral 70,are provided to transmit axial thrust loads from piston 28 to housing12. As previously stated, springs 56 are provided to maintain loading onthrust bearings 70 when the tool is placed in tension.

[0026] A floating piston seal 72 is provided between inner surface 24 ofsecond section 16 of housing 12 and exterior surface 34 of piston 28.Floating piston seal 72 is provided to protect thrust bearings 70 andsprings 56 from abrasive drilling fluids. It also serves a pressurebalancing function placing lubricants which lubricate thrust bearings 70under the same the same hydrostatic pressure as fluids external to thetool. For this purpose ports 71 are provided through housing whichenable drilling fluids to pass into interior bore 26 to exert pressureupon floating piston seal 72. A seal 74 is also provided between innersurface 24 of housing 12 and exterior surface 34 at second end 38 ofpiston 28 to prevent entry of debris or abrasive drilling fluids intointerior bore 26.

[0027] Lubrication ports 76 are positioned along housing 12, in order toadd lubricants after assembly of downhole percussive drilling apparatus10.

[0028] Operation:

[0029] The use and operation of downhole percussive drilling apparatus10 will now be described with reference to FIGS. 1 through 7e. Referringto FIG. 1, during drilling operations piston 28 is rotated withinhousing 12 by downhole motor assembly 40. As piston 28 rotates, springs54 maintain follower surface 44 engaged with cam surface 42. Referringto FIGS. 7a through 7 e, as piston 28 illustrated in FIG. 1, rotates,follower surface 44 alternatively rises up one of inclined planes 50 andthen falls down one of drop offs 52 of cam surface 42. Referring to FIG.1, this imparts a series of percussive hammering impacts to piston 28.The number of percussive impacts per minute that are imparted to piston28 is determined by the speed at which of piston 28 rotate coupled thenumber of drop offs 52 on cam surface 42. It is anticipated that piston28 will rotate within housing 12 at between 90 and 350 rotations perminute. There will be generated approximately 900 percussive impacts perminute with the stroke being approximately ⅛ to ⅜ of an inch.

[0030] Variations: Referring to FIG. 1, in downhole percussive drillingapparatus 10, two sets of springs 54 and 56 were used. First set ofsprings 54 was used to maintain follower surface 44 engaged with camsurface 42 during rotational movement of piston 28 while allowing piston28 limited axial movement. Second set of springs 56 was used to allowthrust bearings 70 to withstand axial loading both when in tension andwhen in compression. Referring to FIG. 6, the purpose of illustratingsecond embodiment 100 is to demonstrate that these functions can becombined to provide a shorter tool. A shorter tool is, of course,desirable when directional drilling tight radius boreholes.

[0031] Referring to FIG. 6, there is provided second embodiment ofdownhole percussive drilling apparatus 100 which includes an elongatetubular housing 112 adapted for insertion down a borehole. With secondembodiment, housing 112 includes only a first section 114, a secondsection 116, and a third section 118. Housing 112 has an outer surface122 and an inner surface 124 which defines an interior bore 126. Apiston 128 is rotatably supported within interior bore 126 of housing112. For ease of assembly, piston 128 is formed from a first section 130and a second section 132. Piston 128 has an exterior surface 134, afirst end 136 and a second end 138. First end 136 is adapted forconnection to a downhole motor assembly 140 that imparts a rotary motionto piston 128 and second end 138 is adapted for connection to a drillbit assembly (not shown).

[0032] As with first embodiment 10, second embodiment 100 includes afirst sleeve 139 and a second sleeve 141 positioned in end to endrelation overlying piston 128 within interior bore 126. First sleeve 129is non-rotatably coupled to inner surface 124 of housing 112 by means ofspline 143. A first engagement surface or cam surface 142 is positionedat one end 145 of first sleeve 139. Second sleeve 141 is non-rotatablycoupled to exterior surface 134 of piston 128 by means of spline 147. Asecond engagement surface or follower surface 144 is positioned at oneend 149 of second sleeve 141. Cam surface 142 and follower surface 144of second embodiment 100 operate in the same manner as with firstembodiment 10. A single set of springs 154 are provided within interiorbore 126. Springs 154 serve to maintain loading on thrust bearings 170when the tool is placed in tension. By virtue of the positioning ofshoulders 167 and 169, springs 154 also serve to force end 145 of firstsleeve 139 engaged with end 149 of second sleeve 141 to maintainfollower surface 144 in engagement with cam surface 142 during rotationof piston 128 and allow for limited axial travel of piston 128 relativeto housing 112 during the percussive hammering impacts. Radial bearingsor bushings 158 are provided to withstand radial loads. Seals 174 areprovided between inner surface 124 of housing 112 and exterior surface134 of piston 128 to limited entry of debris or abrasive drilling fluidsinto interior bore 126. Lubrication ports 176 are positioned alonghousing 112, in order to add lubricants after assembly of downholepercussive drilling apparatus 100.

[0033] Features:

[0034] The downhole percussive drilling apparatus, as described abovehas a number of advantageous features.

[0035] the input power can be produced by a positive displacementprogressive cavity air or mud system;

[0036] the axial and radial bearings are oil lubricated, sealed andpressure balanced to prolong bearing life;

[0037] the apparatus is capable of handling higher radial and axialloads than air hammers—without stalling;

[0038] the torque and impacts per minute can be controlled by theoperator.

[0039] Best Mode Disclosure:

[0040] Some field testing and commercial exploitation of the inventionhas now taken place. It was determined that off bottom bearing 70 wasexperiencing some wear from the hammering action. Referring to FIG. 8, ahydraulic damper, generally identified by reference numeral 200, has nowbeen added to the tool to shield off-bottom bearing 70 from hammeringimpacts. Springs 56 still are used to provide off bottom loading foroff-bottom bearing 70. However, during hammering impacts, hydraulicdamper 200 absorbs the hammering impacts to protect off-bottom bearing70 from wear. The movement which must be absorbed is equal to the axialtravel of piston 28 which is between ⅛ to ⅜ of an inch. Hydraulic damperhas an inner hydraulic housing 202, an outer hydraulic housing 204 andan hydraulic piston 206. Hydraulic piston has a seal 208 which engagesinner hydraulic housing 202 and a seal 210 which engages outer hydraulichousing 204.

[0041] There are a spectrum of rock formations. At one end of thespectrum are hard rock formations. At the other end of the spectrum aresoft rock formations. The remaining rock formations fit somewhere inbetween. During the course of drilling, more than one type of rockformation will be encountered. When drilling through hard rockformations, it is desirable to obtain the maximum hammering impacts thetool is capable of producing. When drilling through soft rockformations, it is better to drill without hammering impacts.

[0042] When drilling through rock formations which are in between softand hard, it may be desirable to adjust the hammering impact. Amechanism has, therefore, been developed which enables the hammeringimpact to be reduced in intensity or turned off. Referring to FIG. 10,first engagement surface 42 is carried by housing 12 and secondengagement surface 44 is carried by piston 28 (as was previouslydescribed). Referring to FIG. 9, springs 56 maintain first engagementsurface 42 and second engagement surface 44 engaged, until sufficientbit weight is placed upon the drill string to overcome the biasing forceof springs 56 and separate the engagement surfaces. As illustrated inFIG. 9, first engagement surface 42 and second engagement surface 44remain engaged, indicating that the hammering action remains on.Referring to FIG. 10, first engagement surface 42 and second engagementsurface 44 are shown as being separated, so that the hammering action isturned off. The best way to understand how this works is to review a fewexamples. We will assume for each of the examples, that springs 56 arepushing first engagement surface 42 and second engagement surface 44together with a force of 10,000 pounds.

EXAMPLE 1

[0043] weight on bit is negligible—therefore, the first engagementsurface 42 and the second engagement surface 44 are fully engaged withthe hammer impact being 10,000 pounds.

EXAMPLE 2

[0044] weight on bit is 5000 pounds—therefore, the first engagementsurface 42 and the second engagement surface 44 are only partiallyengaged, half of the spring force which provides the hammer impact hasbeen negated, with the remaining hammer impact being 5,000 pounds.

EXAMPLE 3

[0045] weight on bit is 9000 pounds—therefore, the first engagementsurface 42 and the second engagement surface 44 are only partiallyengaged, nine tenths of the spring force which provides the hammerimpact has been negated, with the remaining hammer impact being 1,000pounds.

EXAMPLE 4

[0046] weight on bit is 11,000 pounds—therefore, the first engagementsurface 42 and the second engagement surface 44 are fully disengaged,the entire spring force which provides the hammering impact has beennegated.

[0047] In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following the word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one of the elements.

[0048] It will be apparent to one skilled in the art that modificationsmay be made to the illustrated embodiment without departing from thespirit and scope of the invention as hereinafter defined in the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A downhole percussiondrilling apparatus, comprising: an elongate tubular housing adapted forinsertion down a borehole, the housing having an outer surface and aninner surface which defines an interior bore; a piston rotatablysupported within the interior bore of the housing, the piston having anexterior surface, a first end and a second end, the first end beingadapted for connection to a downhole motor assembly that imparts arotary motion to the piston and the second end being adapted forconnection to a drill bit assembly; a first engagement surfacenon-rotatably coupled to and projecting from the inner surface of thehousing into the interior bore; a second engagement surfacenon-rotatably coupled to and projecting from the exterior surface of thepiston into the interior bore; one of the first engagement surface andthe second engagement surface serving as a cam surface and the other ofthe first engagement surface and the second engagement surface servingas a follower surface, the cam surface having a plurality of inclinedplanes each terminating in a drop off such that with each rotation ofthe piston the follower surface rises up each of the inclined planes andthen falls down each of the drop offs of the cam surface therebyimparting a series of percussive hammering impacts to the piston; andsprings within the interior bore between the inner surface of thehousing and the outer surface of the piston to maintain the firstengagement surface and the second engagement surface engaged duringrotation of the piston and allow limited axial travel of the pistonrelative to the housing during the percussive hammering impacts.
 2. Thedownhole percussion drilling apparatus as defined in claim 1, whereinthe biasing force exerted by the springs to maintain the firstengagement surface and the second engagement surface engaged, decreasesas bit weight increases, thereby allowing the force behind thepercussive hammering impacts to be adjusted by altering the bit weight.3. The downhole percussion drilling apparatus as defined in claim 2,wherein the first engagement surface and the second engagement surfacebecome disengaged the bit weight exceeds the biasing force exerted bythe springs to maintain the first engagement surface and the secondengagement surface in engagement.
 4. The downhole percussion drillingapparatus as defined in claim 1, wherein a first sleeve is positioned inthe interior bore which is non-rotatably coupled to the inner surface ofthe housing, the first engagement surface being carried by the firstsleeve; and a second sleeve is positioned in the interior bore which isnon-rotatably coupled to the exterior surface of the piston, the secondengagement surface being carried by the second sleeve.
 5. The downholepercussion drilling apparatus as defined in claim 1, wherein an offbottom bearing is provided and an hydraulic damper is provided to shieldthe off bottom bearing from the percussive hammering impacts.